Adobe 65045315 Photoshop Elements Manual - Page 295

USING PHOTOSHOP ELEMENTS 10 289 Optimizing for the web PNG-24 Like JPEG, this is a good format for photographs. Choose PNG-24 rather than JPEG only when your image contains transparency. (JPEG does not support transparency; you must fill it with a matte color.) PNG-24 files are often much larger than JPEG files of the same image. GIF GIF is the format to use for line art, illustrations with large areas of solid color and crisp detail, and text. Also, if you want to export an animated image, you must use GIF. PNG-8 PNG-8 is a lesser-known alternative to GIF. Use it for the same purposes (except animation). Images in GIF and PNG-8 formats, sometimes called indexed-color images, can display up to 256 colors. To convert an image to indexed-color format, Photoshop Elements builds a color lookup table. If a color in the original image does not appear in the color lookup table, the application either chooses the closest color in the table or simulates the color using a combination of available colors. JPEG and PNG-24 files support 24-bit color, so they can display up to 16 million colors. Depending on the format, you can specify image quality, background transparency or matting, color display, and the method a browser should use to display the image while downloading. The appearance of an image on the web also depends on the colors displayed by the computer platform, operating system, monitor, and browser. You may want to preview images in different browsers and on different platforms to see how they will appear on the web. About the JPEG format The JPEG format supports 24-bit color, so it preserves the subtle variations in brightness and hue found in photographs. A progressive JPEG file displays a low-resolution version of the image in the web browser while the full image is downloading. JPEG image compression is called lossy because it selectively discards image data. A higher quality setting results in less data being discarded, but the JPEG compression method may still degrade sharp detail in an image, particularly in images containing type or vector art. Note: Artifacts, such as wavelike patterns or blocky areas of banding, are created each time you save an image in JPEG format. Therefore, you should always save JPEG files from the original image, not from a previously saved JPEG. Original image (left), and optimized JPEG with Low quality setting (right) The JPEG format does not support transparency. When you save an image as a JPEG file, transparent pixels are filled with the matte color specified in the Save For Web dialog box. To simulate the effect of background transparency, you can match the matte color to the web page background color. If your image contains transparency and you do not know the web page background color, or if the background is a pattern, you should use a format that supports transparency (GIF, PNG-8, or PNG-24). More Help topics "Create a matted GIF or PNG image" on page 296 Last updated 1/2/2012